Such a servo-steering unit with closed center has been disclosed in DE-A1-41 26 020. That kind of servo-steering unit has a linear course of a characteristic line. This means that, in case of elevated servo pressures, that actuating torque can greatly increase.
However, in the servo-steering units with an open center used at present it is customary, starting from a specific pressure in the servomotor, once again to increase slightly the actuating torque. This means that starting from said specific point the characteristic line extends more abruptly. This effect is called "interception" or "actuating-torque limitation".